Stagnant water in water distribution systems for municipalities poses a problem contamination of potable water. Stagnation is found in water piping systems and reservoirs that do not have sufficient flow to keep the water active, where water remains still for long period of time.
Stagnant water in municipal piping systems is a major cause of bad water taste, foul odors in water, discoloration of water, buildup of sediments in residential hot water reservoirs, and bacterial growth in toilet reservoirs and drains of bathroom accessories. Stagnant water can cause many illnesses, such as digestive problems.
Generally, municipal water supply systems are flushed periodically to discharge stagnant water and to eliminate concentrations of chlorine or other disinfectants used in water supply systems which tend to accumulate at regions of low flow.
Another problem associated with low flow or water stagnation in cold climates is the possibility of water freezing in the pipes, which can cause the pipes to crack or burst. Often taps are purposely left open to allow a continuous flow of water so that during the sub-zero temperatures of the winter water will not freeze in the pipes. This of course has the disadvantage of wasting water.
The problems of stagnant water and of freezing are particularly troublesome for air valves, air release valves or air and vacuum valves in pipeline systems.